Try using "Cold Spray" on the adhesive strip on the back of your sealed bubble mailer, it works a treat on the plastic mailers (it takes a lot more effort for the papery mailers though). A good spray across the length of the adhesive strip and then it should just open with little effort and it does not damage the mailer, you may or may not have to use double sided tape to re-seal after this process if you wish to recycle the mailer.